The Origin and Early History of Life Chapter

The Origin and Early History of Life Chapter 4

Where the first cell came from? • • Or…. Can life arise from non-life? Can we test this scientifically? – Conditions on early earth – Formation of organic molecules warm little pond – Chemical evolution – Primitive cell – Prokaryotes – Eukaryotes – Multicellular organisms 2

What do we know? • • ~ 1. 5 Million species identified so far Many more remain unidentified 3

Are we alone? A. Yes B. No 4

Which one represents possible origin of life on earth? A. B. C. D. Extraterrestrial aliens brought it Came with meteors from other planets Some superhuman powers created it Chemicals from primordial soup combined to make life None of the above 5

We don’t know how life originated. Probably arose on Earth, but an alternate theory suggests it arose elsewhere and drifted through space to seed the Earth 6

What does life need? 7

What does life need? A way of harnessing energy to do useful work, • a way of storing and reproducing genetic information, • a way to keep the inside separated from the outside. Which of these arose first is a matter of debate. • Inheritance first or metabolism first? Or both simultaneously? • However, once a genetic system is in place, natural selection will quickly improve the new life form. 8

Some Theories • • • Darwin thought life originated in a “warm little pond”. However, since his time we know that life can exist in a much larger range of environments, and many theories now focus on high temperature and pressure environments such as a the bottom of the ocean or deep underground. The “RNA World”: a theory that puts genetics at the center. Iron-sulfur world: puts metabolism first Clay minerals: life started as selfreproducing clay crystals 9

Origins of Life “The Scientific Story” 10

Prebiotic Earth • Conditions on the primitive Earth were not the same as those present today Image Credit A. I. Oparin • • • No spontaneous generation of life today (Pasteur)… because the necessary conditions no longer exist. © 2010 Paul Billiet ODWS J. B. S. Haldane (credit: Bassano and Vandyk Studios) 11

Origin of the Universe and the Earth • • • Life most likely emerged under high-temperature conditions. 15 billion years ago The “Big Bang” led to the formation of the stars of the “universe” The sun is the closest star to us 4. 6 billion years ago Planets of our solar system were formed including our earth 12

Conditions on Early Earth. Reducing Atmosphere – Early atmosphere is often referred to as a reducing atmosphere on the primitive Earth. No free oxygen (O 2) § exact conditions unknown v ample availability of hydrogen atoms v very little oxygen 13

Conditions of the early earth: • • The Earth’s surface temperature probably hotter than today very hot, barren rock, volcanoes Lightning , ultraviolet radiation gases: Free hydrogen : hydrogen (H 2) (Hydrogen sulfide/Hydrogen cyanide saturated hydrides § methane (CH 4) § ammonia (NH 3) § water vapor (H 2 O) Energy for chemical reactions between these gases could come from electric discharge in storms or solar energy (no ozone layer) 14

Then what? • • • The earth’s temperature cooled over many years resulting in condensation and huge rains. Oceans formed and covered the earth. These oceans were thought to be near boiling point. Chemical Evolution took place, rearranging the atoms of the gases of the atmosphere in to the building blocks of organic compounds. 15

Organic Compound Building Block Protein Amino Acids Nucleic Acids Nucleotides Carbohydrates Simple Sugars Lipids Glycerol and Fatty Acids 16

1950’s Miller-Urey Experiment • • Attempted to reproduce early reducing atmosphere and produce organic compounds from inorganic materials – hydrogen-rich – electrical discharges After a week 15 amino acids in the mixture Other biologically important molecules had been formed including ethanoic acid, lactic acid and urea Later similar experiments were done using CO 2 that produced nucleotides. 17

Urey and Miller • • • Produced – amino acids – carbohydrates – lipids – Nucleotides Conclusion? Perhaps the building blocks of organic compounds could have formed on primitive earth (Chemical Evolution) Image Credit Stanley Miller 18

Conclusion • These experiments cannot reproduce the exact conditions on the primitive Earth • We shall never know exactly what happened • BUT it can be shown that the basic building blocks for the large macromolecules can be synthesised in vitro from inorganic compounds. © 2010 Paul Billiet ODWS 19

Chemical Evolution • • If life originally arose from non-life, how might this have happened? Consider the following scenario – Synthesis and accumulation of small organic molecules – Joining of these monomers into polymers – Aggregation of these molecules into droplets to form localized microenvironments – Origin of heredity 20

The Jump… • • • It is thought that these compounds began to cluster together held by lipid molecules accumulating. . These clusters were called coacervates, or “proteinoid microspheres” Scientists believe that these “abiotic” proteinoid microspheres made the jump to become the • first living cell approximately 3. 5 billion years ago. Spontaneous Generation? ? 21

Polymer Formation • • Sidney Fox (University of Miami) demonstrated the abiotic polymerization of organic monomers Polymers were formed when dilute solutions of organic molecules were dripped onto hot sand, clay, or rock – • • “Proteinoids” - Clay can serve to concentrate these molecules – Monomers bind to charged sites on clay particles - Metal ions in clay have catalytic function 22

From monomers to polymers • • Amino acids into polypeptides, could have occurred when dry or highly concentrated monomers are heated Condensation reactions take place forming peptide bonds between amino acids or phosphodiester bonds form between nucleotides. © 2010 Paul Billiet ODWS 23

Early catalysts • • As molecules adsorb to the clay mineral particles they become concentrated (stick to the surface particles) These clay particles (coacervates) may have been essential catalysts in the formation of polymers. © 2010 Paul Billiet ODWS 24

The first polynucleotides • • • Once formed polynucleotides show a tendency to copy themselves using complementary base pairing This was probably catalysed by the presence of clay particles and metal ions These single stranded polynucleotides would have been the equivalent of RNA. © 2010 Paul Billiet ODWS 25

? Which came first A. DNA Most Likely B. RNA C. Protein DNA (Genetic information) RNA (Information and catalytic) PROTEIN (Catalytic and structural) 26

RNA World • One possible solution to needing both DNA to store genetic information and proteins to carry out activities is to use RNA for both. RNA can store information, and it can act as an enzyme. • • • Perhaps there was a stage in the development of life with nothing but selfreplicating RNA molecules. Proteins, DNA, and cell membranes added later in this scenario. No real evidence for it, but RNA works as an enzyme in some of the most basic life processes, such as making proteins. 27

Abiotic RNA Replication Remember RNA enzymes? 28

The first hereditary information • • • RNA was probably the first hereditary molecule having the ability to copy itself RNA shows enzymic (catalytic) properties called ribozymes Polynucleotides are very good molecules at storing and transmitting information but they lack the versatility for all the chemical functions of a cell. © 2010 Paul Billiet ODWS 29

A great partnership • • Polypeptides, which can form complex 3 -dimensional structures (proteins), are much better at complex cell functions A partnership must have formed polynucleotides and the polypeptides between the • • • The polynucleotides directed the synthesis of the polypeptides Today it is clear that information only flows from polynucleotides to polypeptides. Translation had started. © 2010 Paul Billiet ODWS 30

The origin of DNA • • • Later the hereditary information was probably stored in the form of DNA which is more stable than RNA The passage of information from RNA to DNA is possible in nature The reverse transcriptase enzyme of the retro viruses shows this. © 2010 Paul Billiet ODWS Image Credit: DNA 31

The first membranes, the first cells • • • If a piece of RNA codes for a particularly good protein there is nothing to stop that protein being used by other RNA molecules If however the RNA is enclosed in a membrane then it can keep it’s protein to itself and gains a selective advantage So membranes probably pushed evolution by natural selection forwards. © 2010 Paul Billiet ODWS 32

Membranes defined the first cell • • The phospholipids form lipid bilayers when they are surrounded by water All the components of a simple prokaryotic cell were now assembled They diversified in their metabolism By 2 billion years ago free oxygen was appearing in the atmosphere due to the activity of photosynthetic bacteria. © 2010 Paul Billiet ODWS 33

What did this first cell look like? • The first cell was likely: • Aquatic • Prokaryotic • Anaerobic • Heterotrophic (Oparin and Haldane’s Heterotroph Hypothesis) 34

Biological Evolution now begins • • The following time line describes some of the big events: 2 billion years ago • • photosynthetic prokaryotes evolve releasing O 2 into the atmosphere. This brought about two major changes – Aerobic environment – Formation of ozone (O 3) – UV-rays 2 O 2 O + O + O O 3 + O Aerobic environment led to aerobic organisms evolving With 18 X more energy they could grow faster, reproduce faster and evolve faster. 35

What Happened Next? • • • 1. 5 billions years ago eukaryotes evolved Large prokaryotic cell engulfs a smaller prokaryotic cell. Resulted in the first eukaryotic cell (mitochondria and chloroplasts have their own DNA!!) 36

ENDOSYMBIOSIS BEGINNING OF THE EUKARYOTIC CELLS • • EVIDENCE FOR ENDOSYMBIOSIS DNA Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College. evolution. berkeley. edu/evolibrary/article/0_0_0/endosymbiosis_03 37

• • • What likely followed? - Aquatic multicellularity NFB Evolution - Terrestrial Autotrophs - Terrestrial Heterotrophs How Did Life Begin? How Did Life Begin 2 38

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Iron-Sulfur World • • • A “metabolism first” scenario involves naturally occurring iron sulfide (also called pyrite) crystals. These crystals can catalyze both oxidationreduction reactions (producing energy) and polymerizations of amino acids. Works especially well at high temperatures and pressures, such as are found in deep ocean vents called “black smokers”. Very small pores in the rocks make good chambers that take the place of membranes. An active self-sustaining metabolic system in the absence of inheritance. Some nucleic acids randomly polymerized by the Fe-S crystals eventually colonized the pores and had the property of self-replication. 40

Origin of protobiots • Bubble theories (Oparin) 41

PROTO-CELLS • • • Chemical evolution ultimately led to the formation of proto-cells – Membrane-surrounded sacs containing genetic material and metabolically-active molecules Such structures have been experimentally produced From these proto-cells, cells ultimately arose 42

Earliest Cells • Microfossils have been found in rocks as old as 3. 5 billion years old. – resemble prokaryotes Stromatolites 43

EARLIEST LIFE • • The earliest cells were prokaryotic – Lack a membrane-bound nucleus Early in the history of life, populations diverged into two major lineages – – bacteria archaea & eukaryotes 44

Archaebacteria • Extreme-condition prokaryotes – lack peptidoglycan in cell walls § methanogens § extreme halophiles § extreme thermophiles – thought to have split from Bacteria 2 bya. 45

Bacteria • Second major group of prokaryotes – strong cell walls – simpler gene structure – contains most modern prokaryotes § includes photosynthetic bacteria v cyanobacteria 46

EARLIEST LIFE • How do we know that domain Eukarya is more closely related to domain Archaea than to domain Bacteria? – Analysis of r. RNAs and other highly conserved genes and proteins provide the strongest evidence 47

First Eukaryotic Cells • Eukaryotes probably arose about 1. 5 bya. – Internal membrane-bound structures such as mitochondria and chloroplasts are thought to have evolved via endosymbiosis. § Energy-producing bacteria were engulfed by larger bacteria. v beneficial symbiotic relationship 48

First Eukaryotic Cells • • Sexual reproduction – Eukaryotic cells can reproduce sexually, thus allowing for genetic recombination. § Genetic variation is the raw material necessary for evolution. Multicellularity – arisen many times among eukaryotes § fosters specialization 49

What they have and what they don’t 50

What about this group? 51

That is the end 52

Summary • • Fundamental Properties of Life Origin of Life Hypotheses Chemical Evolution Cell Origin Theories – Bubble Theories Prokaryotic Cells – Archaebacteria – Bacteria Eukaryotic Cells Extraterrestrial Life 53

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Development of new branches on the TREE 55

TAXONOMY 56

Extraterrestrial Life • Universe has 1020 stars similar to our sun. – Conditions may be such that life has evolved on other worlds in addition to our own. § ancient bacteria on Mars. v largest moon of Jupiter, Europa, covered with ice. Ø liquid water may be underneath 57

The Domains and Kingdoms 58

What have we learned so far? • Cell theory – • Molecular basis of inheritance – • DNA encodes genes which make-up and control living organisms. Evolutionary change – • All living organisms are made of cells, and all living cells come from other living cells. Life-forms have evolved varying characteristics to adapt to varied environments. Evolutionary conservation – Some characteristics of earlier organisms are preserved and passed on to future generations. 59

Lets make something with those molecules • • Aggregations of abiotically produced molecules Preceded living cells Laboratory experiments have demonstrated their formation from organic compounds Protobionts and liposomes 60